1. Field of the Invention
The present invention relates to a system and method which use a scanning electron microscope (hereinafter, referred to as a “SEM”) to irradiate a convergent beam of electrons onto a semiconductor and detect electrons emitted from the irradiated position during a pre-process for manufacturing an industrial product, in particular, a semiconductor, thereby acquiring an image of an observation object. In particular, the present invention relates to a system and method for monitoring manufacturing processes which have at least one of a SEM-based semiconductor-wafer inspecting device and a SEM-based semiconductor pattern measuring device which require acquiring a highly magnified image.
2. Description of the Related Art
With the miniaturization of semiconductors, it has been becoming more difficult to control pre-processes of semiconductors. Therefore, it has become difficult to ignore a difference between a dimension of a design pattern and a dimension of a pattern obtained by transferring a pattern to a resist, the difference being causable by an optical proximity effect in an exposure process of a semiconductor. For this reason, an optical proximity correction (hereinafter, refereed to as an “OPC”) is being performed to simulate such an optical proximity effect and correct a mask pattern. In an exposure process using a mask undergone an OPC, hotspots in which defects can easily occur due to a change in a process may be generated. In order to perform a normal manufacturing process without being influenced even by a slight change in a process even if there is the hotspot, a mask layout design should be changed. Design methods for controlling defects causable in manufacturing are known as design for manufacturing (referred to as “DFM”). In order to effectively perform a DMF, it is required a system for smoothly feeding a manufactured state back to a design.
A first exemplary technique of the DMFs is a method in which CAD (computer aided design) data are analyzed to automatically determine points for managing a state of a manufacturing process and images of the points are acquired and observed by use of a microscope such as a SEM, as disclosed in, for example, JP-A-2002-33365.
A second exemplary technique of the DMFs is a method in which detected defects are acquired by inspecting an entire surface or a part of a wafer and are observed at a high magnification by use of a microscope such as a SEM, as disclosed in JP-A-H1 (1998)-135288, and a manufactured state is controlled.
A third exemplary technique of the DMFs is a method in which an image of a semiconductor wafer is acquired, edges of the image are detected, and the edges are compared with designed data, so as to detect systematic defects repeatedly occurring every shot, as disclosed in JP-A-2005-277395. Systematic defects cannot be coped with by a conventional shot comparison.
However, it is difficult to exactly monitor a manufacturing process state of a semiconductor wafer by the above-mentioned general techniques.
In the first exemplary technique in which CAD data are analyzed to automatically determine points for managing a state of a manufacturing process, growth in pattern density of a semiconductor and growth in the size of semiconductor wafers from 200 mm to 300 mm increase the number of management points which should be evaluated, and make exhaustive managing more difficult. For this reason, samples to be evaluated are selected from wafers or chips so as to reduce the number of objects to be evaluated. However, a technique of maximizing an effect with the minimum number of samples has not been established yet. Moreover, a simulation of hotspots based on a lithographic simulation cannot necessarily hinge on all of manufacturing process conditions. For this reason, some omissions can occur in evaluating only hotspots.
Further, in reviewing defects by use of a reviewing apparatus based on the second exemplary technique, it is difficult to review notable defects. Manufacture information important in performing a DMF represents whether a hypothesis made during designing and used for a simulation corresponds to a result obtained by inspection and measurement during actual manufacturing. However, it is difficult to feed defects, such as random foreign materials, which are not closely related to a design, back to the design only by reviewing the defects.
In inspection through comparison between edges and CAD data according to the third exemplary technique, it is difficult to obtain a sufficient throughput. Moreover, it is difficult to inspect the whole chips since edges of an image actually acquired do not necessarily correspond to CAD data.